The present invention relates to a method and a machine for manufacturing a solid electrolytic capacitor; more specifically, a method of encapsulating the electrolytic capacitor elements mounted on a hoop metal lead frame with a molding resin.
A method for manufacturing a solid electrolytic capacitor that uses a conductive high polymer material for the solid electrolyte is described as an example of the conventional manufacturing method, referring to FIG. 6 and FIG. 7. FIG. 6 is a plan view showing part of a hoop metal lead frame mounted with an element for solid electrolytic capacitor. A metal lead frame 16 has a terminal section 18 provided continuously at a certain regular interval along the direction of length, and a crosspiece 19 between respective terminal sections 18 for connecting both sides of the metal lead frame in terms of the width direction. The terminal section 18 is mounted with a capacitor element 17, with electrode of the capacitor element 17 connected to the terminal section 18. A perforation 20 is for transferring the lead frame 16.
FIG. 7 is a partial plan view used to describe a method of encapsulating the capacitor element 17 of FIG. 6 with a molding resin. A main runner 21 lies close to the metal lead frame 16 along one of the sides, and a plurality of sub runner 22 branch-out from the main runner 21 covering every other crosspiece 19. Molding resin is injected from the sub runner 22 through a gate portion 23. The capacitor element 17 is encapsulated with the molding resin forming a solid electrolytic capacitor 24 on the lead frame 16. Removal of the main runner 21 and the sub runner 22 provides finished pieces of the solid electrolytic capacitor.
In the above described conventional method of manufacture, the solid electrolytic capacitors 24 formed on the metal lead frame 16 are connected with the main runner 21, the sub runner 22 and the gate portion 23, as shown in FIG. 7. The first action needed to divide the capacitors 24 into individual pieces is to separate the main runner 21 and the sub runner 22 from the solid electrolytic capacitors 24 formed on the metal lead frame 16. The action of removing the runners 21, 22 generates following problems.
A force exerted to peel the main runner 21 and the sub runner 22 off the metal lead frame 16 inevitably gives an unwanted force to the crosspiece 19 covered with the sub runner 22. The unwanted force ill affects the solid electrolytic capacitors 24. Namely, the tight adhesion between the molding resin and the lead frame 16 is deteriorated, and the hermetic sealing property of the resin-encapsulated capacitor elements 17 is degraded.
A conventional countermeasure taken to solve the above problem is to provide a blasting on the metal lead frame 16 in the area to be covered by the molding resin, for the purpose of increasing the adhesive strength to resin. However, such a countermeasure has not been effective enough to totally eliminate the adverse influence of the force exerted on the solid electrolytic capacitors 24 through said crosspiece 19. So, under the conventional method, it has been difficult to provide a sufficient assurance on the quality of solid electrolytic capacitors 24 with respect to the liermetic sealing property. Meanwhile, if one wants to separate the runners 21, 22 from the metal lead frame 16 without leaving unwanted force on the solid electrolytic capacitors 24, an expensive machine of complicated structure will be required.
The present invention aims to offer a method for manufacturing the solid electrolytic capacitors, as well as a machine for the manufacture, which can provide the solid electrolytic capacitors on the stable basis that are superior in the reliability with respect to the hermetic sealing property.
A method for manufacturing a solid electrolytic capacitor in accordance with the present invention is providing a metal lead frame with a crosspiece between every two capacitor elements along the length direction of the lead frame, providing a sub runner, which is branching out from a main runner, in a region where there is no crosspiece, and injecting a molding resin onto the capacitor elements via the sub runner. Under the above described method of manufacture, since the sub runner is not covering the crosspiece, the lead frame is not affected by unwanted forces when separating both runners from the lead frame on which the capacitor elements have been integrated. Therefore, the hermetic sealing property is not ill affected, and the solid electrolytic capacitors thus manufactured will have a superior reliability.
In the above described manufacturing method of the present invention, it is preferred to provide the metal lead frame with a reference hole at the starting point and the ending point of a span corresponding to a number of capacitor elements that can be molded at one shot, for detecting dislocation in the transfer pitch; and transferring the metal lead frame for the number of capacitor elements accordingly. The reference holes may be detected by a sensor for preventing the transfer pitch dislocation. Thus the molding operation may be conducted efficiently at a higher precision level.
When joining metal lead frames, it is preferred to have the reference hole at the end of a first lead frame and the reference hole at the beginning of a second lead frame coupled together. By joining two metal lead frames in this way, the molding operation may be carried out continuously without halting at the joint of two lead frames, or discarding the molded elements of that sector. This contributes to a further increased productivity and yield rate.
It is also preferred to provide the reference hole at only one side, in terms of the width direction, of a metal lead frame. With this configuration, a reversed lead frame can be easily detected, and the occurrence of a trouble may be prevented.
The metal lead frame having the resin-encapsulated capacitor elements is severed from the sub runner, in a manner where the sub runner is peeled off the metal lead frame while at least the metal lead frame is held firm. Since the sub runner is not covering a crosspiece, no unwanted force is given on the metal lead frame during the severance operation.
A machine for manufacturing a solid electrolytic capacitor in accordance with the present invention comprises transfer means for transferring resin-encapsulated capacitor elements integrated on a metal lead frame molded through a main runner and a sub runner, holding means for holding the metal lead frame from the upper and the bottom surfaces having an escape portion for avoiding making contact with the sub runner, and guiding means disposed at a place in the down stream of the holding means provided for guiding the main runner. The metal lead frame is severed from the sub runner by making use of the holding means. Since the severance is conducted by the guiding means, structure of the present manufacturing machine is quite simple. Thus the solid electrolytic capacitors having a superior hermetic sealing property can be manufactured for an inexpensive cost with ease.
A metal lead frame used in the manufacturing method of the present invention is provided with a plurality of terminal sections stretching in terms of the width direction, being disposed along the length direction, and a plurality of crosspieces bridging the both sides in terms of the width direction, being disposed one crosspiece for every two terminal sections along the length direction.